Saint Mary's (21-8, 13-5) clinched 2nd place in the West Coast Conference Thursday, but now has lost two of its last three games. The Gaels open in the quarterfinal round Saturday in Las Vegas.
Santa Clara (13-17, 7-11) opens the tournament Friday.
Jarvis Pugh dunked to tie the game at 67-67 with 2:45 left, but Aaron Bright drilled a 3-pointer to give Saint Mary's a 70-67 lead. Brandon Clark drew a foul and converted two free throws with 1:01 left to cut the deficit to 70-69. Brad Waldow missed a layup with :32 left and Desmond Simmons missed a tip-in before Brownridge hit the game-winner.
Brandon Clark scored 21 points and Brownridge and Denzel Johnson each added 17.
Kerry Carter scored 19 points to lead Saint Mary's.